Modern advanced technology extensively requires various sorts of machine elements including rolling-contact bearings and linear motion guide systems. Especially, the linear motion guide systems have become popular in a diversity of machines including semiconductor production machines, various assembly machines, and so on, which are needed to work with high performance in operating speed and cycle. To cope with this, machine elements, especially the modern linear motion guide systems are also required to make smooth motion with less noise to live up to high moving velocity and high cyclic operation of the machines.
With the rolling guide units used in the conventional linear motion guide systems, a diversity of separators has come to practical use in the circulating circuits to keep the rolling elements against direct contact with each other. Among the prior separators used in the linear motion guide systems, a flexible separator is known in which the separator is allowed to deform elastically for itself to regulate any interval between any two adjacent rolling elements. Recent operating environment for the linear motion guide systems, nevertheless, is looking to the separator that is rich in mechanical stiffness even though flexible in elastic deformation.
In the commonly assigned Japanese Patent Laid-Open No. 2001-124075, there is disclosed a rolling guide unit in which separators are placed between any leading and trailing rolling elements, the separators being each composed of a major central body and elastic supports arranged around the major central body on axially opposite circular edges, three on each edge, in such a way that any two adjoining supports are raised oppositely to each other in the axial direction of the separator, making it possible to compensate for the variances in length of the circulating passage with the separator upon loading of the rolling elements in the circulating circuit. With the rolling guide unit constructed as stated earlier, the separator lying between any two adjacent rolling elements is especially composed of the major central body and elastic supports extending radially around the major central body, the elastic supports being made up of elastically deformable parts made around the periphery of the major central body and distal seats integral with the elastically deformable parts so as to spread in radial direction. The separator comes into engagement with the associated rolling elements at only the distal seats thereof when the pressure exerted on the rolling elements to press them against each other is relatively less. In contrast, when the pressure recited earlier is larger, the elastically deformable parts get back to bring the separator into close engagement with the associated rolling elements around the circular periphery thereof.
An elastic spacer for ball bearings is disclosed in U.S. Pat. No. 4,761,820 (JP Laid Open No. S63-111316) in which the spacer is inserted between adjacent balls in such a way making a substantially punctiform contact with any one of the adjacent balls while a circular-line contact with another rolling element. The prior elastic spacer has an outer contour inscribed in a cylinder and its length corresponding to at least one half the diameter of the ball. The spacer also has in its bore a conical partition which, in its central region contiguous to the cone tip, is subdivided into elastically resilient tongues by slots extending approximately radially, one ball making approximately punctiform contact and the other ball abutting on the partition in a contact circle.
Another linear motion guide system is disclosed in Japanese Patent Laid-Open No. 2003-239964, in which a separator is designed to have enough resilient force without using any specific material rich in elasticity to ensure the improvement in working performance of the linear motion guide system, which is composed of a guide rail, a slider movable relatively to the guide rail, and more than one rolling element allowed to roll through a circulating circuit made up of a load-carrying race and a non-loaded return passage. The separator interposed between any two adjacent rolling elements is made on opposite sides thereof with circular surfaces where the rolling elements make rolling-contact with there. The circular surfaces are each made to an arc of contact different from one another.
In another Japanese Patent Laid-Open No. 2003-222128, there is disclosed a unidirectional actuator in which rolling elements or balls are kept against collision, which might otherwise any noise or adverse vibration, to thereby improve the durability. With the unidirectional actuator recited earlier, separators of synthetic resin are interposed between any leading and trailing rolling elements to keep the rolling elements against collision with one another during traveling motion.
Nevertheless, the separator in the rolling guide unit disclosed in the commonly assigned senior Japanese patent application recited earlier, through rich in resiliency or elasticity, is forced to make the elastically deformable area thereof small in return for encouraging the mechanical stiffness or rigidity. Moreover, the elastic spacer for ball bearings recited earlier is lack of flexibility for elastic deformation, and apt to get an interval between the adjoining rolling elements more spreading out, so that the rolling elements lying in the load-carrying area are reduced in number, with the result of reduction in their load capacity. Besides, the elastic spacer made as stated earlier is complicated in construction and, therefore, very tough in production. With most linear motion guide units constructed as stated earlier, the prior separator interposed between the leading and trailing rolling elements is made to come on the opposite circular surfaces thereof into rolling contact with the rolling elements at local areas asymmetric with one another on the opposite circular surfaces. As a result of the asymmetric contact with the rolling elements on the opposite circular surfaces, the prior separator is less in amount of elastic deformation than it should be for large force to deform elastically the separator. Such prior separator is more likely to develop a problem for the following accuracy desired for a roll-contact working on the associated rolling elements